The current development towards truly mobile computing and networking has brought on the evolvement of various access technologies which provide the users with access to the Internet when they are outside their own home network. At present, wireless Internet access is typically based on either Wireless LAN (WLAN) technology or mobile networks, or both.
Wireless LAN systems are typically extensions of a wired network, providing mobile users with wireless access to the wired network. In wireless LAN technology, two basic network topologies are available for network configuration: an ad-hoc network and an infrastructure network. An ad-hoc network is formed by two or more independent mobile terminals (commonly referred to as “clients”) without the services of a base station, i.e., in an ad-hoc network the terminals communicate on a peer-to-peer basis. An ad-hoc network is normally formed for temporary purposes. The infrastructure network, in turn, comprises one or more wireless base stations, called access points, which form part of the wired infrastructure. In this type of network, all traffic goes through the access points, regardless of whether the traffic is between two terminals or a terminal and the wired network, i.e., the mobile terminals do not communicate on a peer-to-peer basis. The mobile terminals are provided with wireless LAN cards, whereby they can access the wired network, such as the Internet, through said access points, which are mainly located in various hot spots, such as airports, convention centers, railway stations, or shopping malls.
The Institute for Electrical and Electronics Engineers (IEEE) has developed a set of Wireless LAN standards for over-the-air modulation techniques used in Wireless LAN systems. These standards are referred to as “IEEE 802.11” (commonly referred to as the “Wi-Fi” standard). The 802.11 standards are actually a family of versions that have developed over the years since 1997. For example, the original version of the standard IEEE 802.11 (commonly denoted as “802.11”) was released in 1997 followed by amendments to the standard IEEE 802.11, which are indicated by “802.11b”, “802.11a” and “802.11g.” These standards (802.11b, 802.11a and 802.11g) use either the 2.4 gigahertz (GHz) band or the 5 GHz band. Further, these standards (802.11b, 802.11a and 802.11g) divide the frequency spectrum into a particular number (e.g., 14) of overlapping, staggered channels. Only selected channels (e.g., channels 1, 6 and 11) are used by these standards, which are spaced apart from one another in a manner that reduces the likelihood of interference. Typically, these standards (802.11b, 802.11a and 802.11g) use a bandwidth of 22 megahertz (MHz). That is, the channels that they use are 22 MHz wide channels.
In January 2004, IEEE announced that it had formed a new 802.11 Task Group (TGn) to develop a new amendment to the 802.11 standard for Wireless LAN. The new standard is referred to as “802.11n.” 802.11n builds upon previous 802.11 standards by adding multiple-input multiple-output (MIMO), which uses multiple transmitter and receiver antennas to allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity, perhaps through coding schemes like Alamouti coding. 802.11n, by definition, must be backward compatible with the prior versions 802.11b, 802.11a and 802.11g, which are defined to use 22 MHz wide channels in either the 2.4 GHz band or the 5 GHz band. There are two competing proposals for meeting the 802.11n specifications: WWiSE (World-Wide Spectrum Efficiency) and TGn Sync. TGn Sync has proposed using 40 MHz wide channels in order to meet the 802.11 specifications. That is, TGn Sync has proposed using 40 MHz wide channels in order to handle the additional data being transmitted and received. However, by using 40 MHz wide channels instead of using 22 MHz wide channels in the 2.4 GHz band, interference (illustrated and discussed further below in connection with FIG. 1) will result between multiple channels being used to support the 40 MHz wide channels. Because there will be interference between the multiple channels being used to support the 40 MHz wide channels, there may be interference between mobile terminals (clients) accessing the Wireless LAN through adjacent access points where the clients are in the same coverage area of a particular access point. Such interference resulting from having 40 MHz wide channels is illustrated in FIG. 1.
FIG. 1 is a plot of frequency versus radio strength illustrating the use of both 22 MHz wide channels and 40 MHz wide channels for the 802.11b, 802.11a, 802.11g and 802.11n standards. As stated above, 802.11b, 802.11a and 802.11g standards use 22 MHz wide channels. FIG. 1 illustrates these standards using channels 1, 6 and 11 in the 2.4 GHz (2400 MHz) band where each of these channels is 22 MHz wide as indicated by the non-shaded area. In particular, these standards may use channel 1 (centered at 2412 MHz) with a bandwidth of 22 MHz ranging from 2401 MHz to 2423 MHz. These standards may further use channel 6 (centered at 2437 MHz) with a bandwidth of 22 MHz ranging from 2226 MHz to 2448 MHz. These standards may further use channel 11 (centered at 2462 MHz) with a bandwidth of 22 MHz ranging from 2451 MHz to 2473 MHz.
As further stated above, the 802.11n standard is proposed to use 40 MHz wide channels. FIG. 1 illustrates the use of 802.11n standard using channels 3 and 8 (use these channels in order to support a bandwidth of 40 MHz) that are 40 MHz wide as indicated by the shaded area. As illustrated in FIG. 1, there is an overlapping of channels 3 and 8 (near channel 6) when 40 MHz wide channels are used in the 802.11n standard. However, there is no overlapping of channels 1, 6 and 11 when 22 MHz wide channels are used for the 802.11b, 802.11a and 802.11g standards. Hence, there will be interference between multiple 802.11n channels if 40 MHz wide channels are used using the same band as the previous 802.11b, 802.11a and 802.11g standards. Because there will be interference between multiple 802.11n channels, there may be interference between mobile terminals (clients) accessing the Wireless LAN through adjacent access points using the 802.11n standard where the clients are in the same coverage area of a particular access point.
Therefore, there is a need in the art for handling the interference between multiple 802.11n channels in a location where there are a small number of available channels.